CNC Project for Simple Bracket: Basic G-Code Example

A CNC project for a simple bracket involves writing a G-code program that includes commands for drilling holes and milling the bracket shape. The program typically uses G00 for rapid moves, G01 for cutting moves, and M30 to end the program.

Syntax

The basic CNC G-code syntax for a simple bracket includes:

• G00: Rapid positioning (move quickly without cutting)
• G01: Linear interpolation (cutting move at set feed rate)
• M03: Spindle on clockwise
• M05: Spindle stop
• M30: Program end and rewind
• X, Y, Z: Coordinates for tool position
• F: Feed rate (speed of cutting)

gcode

N10 G21         (Set units to millimeters)
N20 G90         (Absolute positioning)
N30 M06 T1      (Tool change to tool 1)
N40 M03 S1000   (Spindle on clockwise at 1000 RPM)
N50 G00 X0 Y0   (Rapid move to start position)
N60 G01 Z-5 F100 (Cut down to depth 5mm at feed 100)
N70 G01 X50 Y0  (Cut along X axis)
N80 G01 X50 Y30 (Cut along Y axis)
N90 G01 X0 Y30  (Cut back along X axis)
N100 G01 X0 Y0  (Complete rectangle)
N110 G00 Z100   (Retract tool)
N120 M05       (Spindle stop)
N130 M30       (End program)

Example

This example program mills a simple rectangular bracket with four holes. It drills holes first, then mills the outer shape.

gcode

N10 G21         (Set units to millimeters)
N20 G90         (Absolute positioning)
N30 M06 T1      (Tool change to drill)
N40 M03 S1200   (Spindle on clockwise at 1200 RPM)
N50 G00 X10 Y10 (Rapid move to first hole)
N60 G81 R2 Z-10 F75 (Drill cycle: retract 2mm, drill 10mm deep at feed 75)
N70 X40 Y10     (Second hole)
N80 X40 Y40     (Third hole)
N90 X10 Y40     (Fourth hole)
N100 G80       (Cancel drill cycle)
N110 M05       (Spindle stop)
N120 M06 T2    (Tool change to mill)
N130 M03 S1500 (Spindle on at 1500 RPM)
N140 G00 X0 Y0 (Rapid move to start milling)
N150 G01 Z-5 F100 (Cut down 5mm)
N160 G01 X50 Y0
N170 G01 X50 Y50
N180 G01 X0 Y50
N190 G01 X0 Y0
N200 G00 Z100  (Retract tool)
N210 M05      (Spindle stop)
N220 M30      (End program)

Common Pitfalls

Common mistakes when creating CNC projects for simple brackets include:

• Forgetting to set units with G21 or G20, causing wrong dimensions.
• Not using absolute positioning G90 or relative G91 correctly, leading to unexpected tool paths.
• Skipping spindle start M03 or stop M05 commands, which can damage tools or workpieces.
• Not retracting the tool before rapid moves, risking collisions.
• Incorrect feed rates causing poor surface finish or tool breakage.

Example of a wrong move without retract:

gcode

N50 G01 Z-5 F100  (Cut down 5mm)
N60 G00 X50 Y0     (Rapid move without retract - dangerous)

Correct way:
N50 G01 Z-5 F100
N60 G00 Z100       (Retract first)
N70 G00 X50 Y0

Quick Reference

Command	Description
G00	Rapid positioning (move fast without cutting)
G01	Linear cutting move at feed rate
G21	Set units to millimeters
G90	Absolute positioning mode
M03	Spindle on clockwise
M05	Spindle stop
M30	End program and rewind
F	Feed rate (speed of cutting)
X, Y, Z	Coordinates for tool position

Key Takeaways

Always set units and positioning mode at the start of your CNC program.

Use spindle start and stop commands to protect tools and workpieces.

Retract the tool before rapid moves to avoid collisions.

Drill holes before milling the bracket shape for efficiency.

Check feed rates to balance cutting speed and surface finish.